Effects of packing density, flow and humidity on the performance of needle trap devices

Abstract

Needle trap devices (NTDs) have become a promising alternative to solid-phase microextraction (SPME)due to their robustness and exhaustive sampling while maintaining all the advantages of SPME. This studyinvestigates the compromise required in packing NTDs starting from the hypothesis that their diametermakes perfect packing impractical. The most limiting parameter of NTDs is the small amount of sorbentthat can be fitted in the trap. On evaluating packing density, it is found that the densest packing cannotpractically be achieved with NTDs. This poor packing leads to oscillations in the fluid flow profiles andso sampling flows up to 10-15 mL min−1are recommended for this methodology. The limited amount ofsorbent materials inside the needles makes breakthrough another limiting aspect of NTDs. However, oneof the most significant advantages of these devices is that they have a large preconcentration factor, whichresults in method detection limits in the pptv range with sample volumes <100 mL. This methodologygives promising results in the analysis of water saturated samples as the limited amount of sorbentsreduces water retention. Moreover, it is desirable for a small amount of water to be retained with NTDsas this improves the desorption of the retained compounds in the GC injector and allows sharper injectionband-widths to be obtaine